I see Levitz, from hints dropped in several places in the lettercolumns (and occasionally elsewhere), as being far less than fierce about defending the quality of his earliest writing for DC. That would include the first nearly-two-year stint on the Legion, the "Karate Kid" series, and briefer work on other titles.
He seemed, to me, to admit that this was when he was learning the comics writing craft, and was far from always on top of the many threads of the Legion tapestry. He picked up enough savvy to untwist the multi-issue mess of the Reflecto story, and then went on to thrive in creative combination with several artists -- first Broderick, but then the early Giffen, most of all.
I doubt it's envy that stopped any notion of a "Superboy's Legion" sequel, which if it kept the same creators, would have been as superb as the first go-round.
DC seems, instead, to have gotten this buzz in its collective head against Elseworlds works. Prestige fears, about diluting their icons? Corporate cost-cutting? Too much supervision of creative egos? Who knows. Perhaps all of the above.
